The objectives of this project are to identify the control mechanisms for the development of Adriamycin resistance in mammalian cells in culture and to identify the protein or proteins responsible for such resistance. Adriamycin resistance is primarily mediated through restriction at the cell membrane and Adriamycin-resistant cells release the drug more rapidly than Adriamycin-sensitive cells. The marker for Adriamycin resistance has been successfully rescued from radiation-killed cells by fusion of such cells with viable Adriamycin-sensitive cells. A marker chromosome with a long q-arm, chromosome number 8, has been identified as associated with Adriamycin resistance. The increased chromosomal material bands with giemsa/trypsin rather than staining homogeneously. A first estimate for the DNA segment responsible for Adriamycin resistance gives a sequence of ca. 760 base pairs.